1. Field of the Invention
This invention relates to a method for flocculating finely divided solids suspended in nonpolar liquids and to chemical compositions which are useful in such method.
2. Description of Related Art
The process of flocculation is widely known and used in the treatment of water and waste water. Through the use of flocculation, finely divided suspended particles are agglomerated to permit improved separation by sedimentation, filtration, or other conventional techniques. A general discussion of flocculation is found in PERRY'S CHEMICAL ENGINEERS' HANDBOOK, 4th. Ed., which is incorporated by reference herein. While the process of flocculation is widely known and practiced in the treatment of water and waste water, the chemicals, compounds and polymers that function well as flocculants in aqueous systems are not generally effective for use in such nonpolar solvents as liquid hydrocarbons.
Liquid hydrocarbons and other nonpolar solvents are widely used for removing oily soils and in other processes whereby they become contaminated with finely divided suspensions of soil particles, carbon particles, tar, carbonized hydrocarbons, and the like. One example of such contamination occurs in solvents used in automotive parts washers. Often a substantial portion of the contaminants are so small that they are present as a colloidal suspension and are not readily removed by settling or filtration.
Prior art flocculants and flocculating methods have previously been disclosed, for example, in U.S. Pat. Nos. 4,038,176; 4,230,839; 4,584,111; 4,745,154; 4,778,813; and 5,130,358.
U.S. Pat. No. 4,038,176 discloses and claims the use of soluble cationic polymers as flocculants for the coagulation of colloidal suspensions in oil, particularly used motor oil. The preferred polymer is an oil soluble polymer having a molecular weight of at least 10,000 which is selected from the group consisting of polymers of fatty diallyl quaternary ammonium salts and fatty acid salts of polymers of tertiary amino substituted acrylamides.
U.S. Pat. No. 4,230,839 discloses and claims polymers of quaternary ammonium adducts that are useful for clarifying water containing oil or suspended solids and especially oil-coated solids.
U.S. Pat. No. 4,584,111 relates to the use of an acrylamide polymer to aid in the removal of colloidal particles generated in the manufacture of lubricating oil additives such as zinc salts of dihydrocarbyldithiophosphoric acid and calcium phenate. More particularly, the patent discloses and claims introducing at least a flocculating amount of a water-in-oil emulsion of a water-soluble vinyl addition macromolecular polymer into a hydrocarbon oil reaction system (containing as little as 0.1% water) to flocculate insolubles and reduce haze. A preferred polymer for use in the invention is a cationic charge density polymer such as a methyl chloride quaternized copolymer of di-methyl ammonium ethyl methacrylate and acrylamide.
U.S. Pat. No. 4,745,154 discloses a water-in-oil emulsion comprising an oleophilic continuous phase and an aqueous dispersed phase containing a water soluble copolymer composition obtained by polymerizing in a water-in-oil emulsion a monomer system comprising an addition copolymerizable surfactant monomer and at least one water soluble vinyl monomer. Water soluble cationic monomers such as dimethyl amino ethyl acrylate, dimethyl amino ethyl methacrylate, dimethyl amino ethyl acrylate methyl chloride, dimethyl amino ethyl acrylate dimethyl sulfate, dimethyl amino ethyl acrylate acetate, dimethyl amino ethyl methacrylate methylchloride, dimethyl amino ethyl methacrylate dimethyl sulfate, dimethyl amino ethyl methacrylate acetate, methacrylamino-propyl trimethyl ammonium chloride, etc., are disclosed. Utility of the dimethyl amino ethyl acrylate copolymer as a flocculant is also disclosed.
U.S. Pat. No. 4,778,813 discloses and claims a method of flocculating solids from an aqueous system containing suspended or dissolved solids, the method comprising adding to the aqueous system a flocculant comprising one or more polymeric quaternary ammonium compounds in an amount sufficient to cause the flocculation of the solids.
U.S. Pat. No. 5,130,358 discloses hydrophilic cationic polymer compositions for use as flocculating agents, for flotation of minerals, or for recovery of oil waste in aqueous systems. The subject polymers preferably comprise amino or quaternary ammonium groups. The cationic monomers used in making the polymers can include any conventional anion, preferably a halide ion. Also disclosed and claimed are water miscible compositions comprising a hydrophilic cationic polymer free from anionic monomer components, an anionic surfactant containing at least one lipophilic hydrocarbon residue of at least 9 carbon atoms and at least one hydrophilic anionic group, a water-immiscible oil in which the polymer is insoluble, and a lipophilic non-ionic surfactant which is capable of functioning as a water-in-oil emulsifier. The anionic surfactant can comprise partial alkyl esters of phosphoric acid.
Nonpatent literature relating to flocculation is summarized in the report dated Apr. 19, 1993, prepared by NERAC, Inc., titled "Flocculation In Solvents."
Other prior patents disclose the use of cationic surface active agents, cationic acrylamide polymers with quaternary amine functionality, and imidazolines in different applications.
U.S. Pat. No. 4,576,743 discloses a lithographic plate cleaner comprising cationic surface active agents such as alkyl-dimethylbenzylammonium chloride or amphoteric surface active agents such as an alkylimidazoline, in combination with a nitrate, sulfate, phosphate, or the like, and a wetting agent such as a glycol. The cationic surface active agent is used in an amount ranging from 0.01 to 10% by weight of the plate cleaner.
U.S. Pat. No. 4,783,513 discloses and claims water soluble cationic acrylamide polymers having relatively uniform cationic quaternary amine functionality.
U.S. Pat. No. 4,865,614 discloses the use of quaternary 2-alkyl-2-imidazolinium salts for softening fabrics. Preferred solvents for use in preparing the imidazolines include mixtures of water and short chain alcohols.
Notwithstanding the compositions and methods disclosed in the prior art, a method for flocculating fine, solid particles in nonpolar solvents is therefore needed.